Look like interesting devices.
Certainly solid state pre-amp "valves" have been produced before (and not really set the world alight), but I've not seen a solid-state power "valve" before, although this of course could be due to ignorance on my behalf.
The filament current draw is intriguing, as is the maximum cathode/ heater voltage rating, as solid state devices (usually) don't have heaters.
The transfer characteristic of a MOSFET look not dissimilar to a power pentode/ beam tetrode, however there is no equivalent of the screen grid in a MOSFET, and the a key feature of these devices is that they seem to have a "screen grid". I can't think how this has been achieved, and will apply some thought to it.
It says it can take 800V on plate and screen and 50W dissipation, so the 6L6WS would have the potential to deliver much more power than a conventional 6L6, perhaps as much as 150W for a push pull pair.